The present invention relates to improvements in casters for use on pieces of furniture, dollies and the like.
German Offenlegungsschrift No. 29 35 058 discloses a caster wherein the prongs which flank and support the wheel form part of a bifurcated frame and such frame further includes a web which connects the two prongs to each other and extends between the upper and lower sections of a bearing defining a swivel axis about which the frame can turn relative to its carrier, e.g., relative to a plate which is affixed to the leg of a table, chair, cabinet or the like. The two sections of the bearing are made of sheet steel and are secured to each other by pressing or by resorting to another material deforming technique. A first annulus of antifriction rolling elements is disposed between the web and the upper section of the bearing, and a second annulus of rolling elements is confined between the web and the lower section of the bearing. The web and the two sections of the bearing are formed with tracks for the respective annuli of rolling elements. Such annuli surround a centrally located passage which is defined in part by the bearing and in part by the frame and serves to receive a shaft around which the frame can swivel when the caster is in use.
German Offenlegungsschrift No. 31 36 262 discloses a caster wherein the web of the frame for the wheel is formed with a centrally located bore for a stub and carries a plate-like member which is affixed to the frame by screws. Such screws extend into radial recesses of the plate-like member and the recesses further receive protuberances which are provided on the web. The plate-like member has an upwardly extending annular marginal portion which defines tracks for upper and lower annuli of spherical antifriction rolling elements which are confined in suitable cages. The upper annulus of rolling elements contacts the annular surface of a connecting plate having a cupped extension projecting below the lower annulus of rolling elements. The just described thrust bearing is held together by projections which are provided on the connecting plate, which extend through holes in the cupped extension and which are bent over to prevent separation of the numerous component parts of the axial thrust bearing from each other.
A drawback of the just described conventional casters is that the thrust bearings between the forked frame and its carrier employ expensive antifriction rolling elements and must be machined with a high degree of precision in order to establish adequate tracks for the rolling elements. Moreover, such conventional thrust bearings consist of large numbers of parts which contributes to the cost and complexity of assembly of the caster. The parts must be made of expensive materials in order to ensure that the caster will be capable of standing long periods of use. As a rule, the parts of such axial bearings must be made of steel or an equivalent alloy even if the casters are not expected to be subjected to pronounced stresses.